High Voltage Gas Insulted Switchgear (GIS) Field Testing According to IEEE C37.122

Dyson

04/07/2025 09:26:08

High Voltage Gas Insulted Switchgear (GIS) Field Testing According to IEEE C37.122

The final assembly of the gas - insulated substation (GIS) takes place in the field. This is where all the diverse components that make up the GIS are brought together for the first time. Even if it were possible to fully assemble the GIS in a factory, it would still have to be disassembled for transportation, shipped, and then reassembled at the installation site.
The objective of the field tests is to confirm that all GIS components function satisfactorily both electrically and mechanically after being assembled at the job site. These tests offer a means of demonstrating that the GIS apparatus has been correctly assembled and wired and will operate as expected.

Mechanical Tests: Gas Leakage and Gas Quality (Moisture, Purity, and Density)
Gas Leakage Test：All gas compartments of the GIS must be filled with sulfur hexafluoride gas (SF6) or the required gas mixture up to the manufacturer - specified rated filling pressure. Subsequently, a test is carried out to detect any gas leaks. An initial inspection is conducted to identify all potential gas leakage points and ensure compliance with the specified maximum gas leak rate. This gas leak test should cover all enclosure flanges, enclosure welds, as well as all gas monitoring devices, gas valves, and interconnecting gas piping that have been assembled at the job site.
Moisture Content Measurement：The moisture content of the gas needs to be measured before the GIS is energized. To obtain a reliable measurement, the moisture content should be measured after a period of time following filling, as recommended by the manufacturer. The moisture content must not exceed the limit set by the manufacturer or the value agreed upon between the manufacturer and the user, whichever is lower.
Gas Purity Verification：Prior to energization, the purity of the gas, expressed as a percentage of SF6, must be verified. The gas purity should meet the requirements specified by the manufacturer.
Gas Density Measurement：The density of the gas should be measured and confirmed to be in line with the manufacturer's nominal rated filling requirements.

2. Electrical Tests: Contact Resistance

Main Current - Carrying Circuits：Contact resistance measurements of the main current - carrying circuits are required for each bus connecting joint, circuit breaker, disconnect switch, grounding switch, bushing, and power cable connection. These measurements are used to demonstrate and verify that the resistance values are within the specified limits.
GIS Enclosure Bonding
Connections (for Isolated Phase Bus)：In cases where an isolated (single) - phase bus is utilized, contact resistance measurements also need to be performed on the GIS enclosure bonding connections. The resistivity measurements should not exceed the maximum permissible values as per IEEE Std C37.100.1.

3. Electrical Tests: Low - Frequency AC Voltage Withstand Test

The gaseous and solid insulation (dielectrics) within the gas - insulated substation (GIS) must undergo the application of a low - frequency conditioning voltage. The frequency of this conditioning voltage ranges from 30 Hz to 200 Hz, and it is applied at voltage levels and for durations as specified by the manufacturer. After the conditioning voltage application, a one - minute low - frequency (30 Hz to 200 Hz) voltage withstand test is carried out.

This one - minute low - frequency voltage withstand test is conducted at 80% of the rated low - frequency withstand voltage that was tested in the manufacturer's factory. The objective of these high - voltage tests is to confirm several aspects. Firstly, it verifies that the components of the gas - insulated substation have endured the shipment process without damage. Secondly, it ensures that all components have been correctly assembled. Thirdly, it checks that no foreign or extraneous material has been left inside the enclosures during the assembly process. Ultimately, these tests prove that the GIS is capable of withstanding the test voltage, thereby validating its integrity and performance.

4. Electrical Tests: AC Voltage Withstand Requirements and Conditions

Voltage withstand tests must be conducted between each energized phase and the grounded enclosure. For enclosures housing all three phases, each phase shall be tested individually, with the enclosure and the other two phases grounded. Prior to commencing voltage withstand tests, all power transformers, surge arresters, protective gaps, power cables, overhead transmission lines, and voltage transformers must be disconnected. Voltage transformers can be tested up to the saturation voltage of the transformer at the test frequency.

5. Electrical Tests: Low - Frequency AC Voltage Withstand Requirements and Conditions

Voltage withstand tests are to be carried out between each energized phase and the grounded enclosure. In enclosures with all three phases, each phase should be tested one at a time, while the enclosure and the other two phases are grounded. The insulation between each pair of phase conductors does not require any additional field voltage withstand tests.

Before starting voltage withstand tests, all power transformers, surge arresters, protective gaps, power cables, and overhead transmission lines must be disconnected. Voltage transformers should be tested up to their saturation voltage at the test frequency.

Isolating sections of the GIS apparatus can offer an added advantage of field - testing the open gap of some disconnecting switches, though such a field test is not obligatory. Additionally, it may be necessary to isolate sections of the GIS to facilitate the location of a disruptive discharge or to limit the energy potentially released during a disruptive discharge.

A partial discharge measurement can be performed to detect any possible intrusion of conductive particles or damage to high - voltage insulating components that might have occurred during factory testing, transportation, or installation. The gas - insulated switchgear should be essentially free of partial discharge. The procedure for partial discharge measurement and its interpretation should be provided by the manufacturer and agreed upon between the user and the manufacturer.

6. Electrical Tests: DC Voltage Withstand Tests

DC voltage withstand testing is not advisable for a completed GIS. However, it might be necessary to conduct a DC voltage withstand test on power cables connected to a GIS. These test voltages would inevitably be applied from the end of the cable opposite to the GIS, thus subjecting a small part of the GIS to the DC voltage. It is recommended to keep the portion of the GIS exposed to this DC voltage as small as possible. The manufacturer should be consulted before conducting these tests.

7. Electrical Tests: Tests on Auxiliary Circuits

Dielectric, continuity, and resistivity tests should be carried out on all interconnecting control wiring installed in the field.

8. Mechanical and Electrical Functional and Operational Tests

After the GIS has been assembled at the job site, the following aspects need to be verified:

The torque value of all bolts and connections assembled in the field must be checked to ensure compliance with the specified requirements.
The control wiring should be verified to conform to the schematic and wiring diagrams.
The proper functioning of each electrical, pneumatic, hydraulic, mechanical, key - operated, or combined interlock system needs to be verified for correct operation in both permissive and blocking conditions.
The proper operation of controls, gas, pneumatic, and hydraulic monitoring and alarming systems, protective and regulating equipment, operation counters, including heaters and lights, must be confirmed.
Each mechanical and electrical position indicator for each circuit breaker, disconnect switch, and grounding switch should be verified to accurately indicate the device's open and closed positions.
The gas zones, gas zone identification, gas valves, gas valve positions, and interconnecting piping should be verified to be in line with the physical drawings.
The operating parameters such as contact alignment, contact travel, velocity, opening time, and closing time of each circuit breaker, disconnect switch, and grounding switch must be verified according to the specified requirements.
The correct operation of compressors, pumps, auxiliary contacts, and anti - pump schemes should be verified to meet the specified requirements.
The circuit breakers need to be trip - tested at minimum and maximum control voltages to confirm correct operation.
The secondary wiring should be verified to have correct wire lugs, proper crimping, tightened terminal block screws, correct wire and cable markers, and wiring in accordance with the manufacturer's drawings.

Connecting the GIS to the Electrical System

Once the gas - insulated substation has been fully installed, wired, and all field tests have been successfully completed, the new apparatus is ready to be connected to the existing electrical system. This process involves another set of tests to verify protective relay operation, the ability of circuit breakers to trip upon remote command, and proper phase relationships with various transmission lines. This second series of tests is expected to be similar, if not identical, to the tests carried out on an air - insulated substation (AIS).

References:

IEC 6227-1 (2011) High-Voltage switchgear and Controlgear – Part 1: Common Specifications.
IEEE C37.122 (2010) IEEE Standard for Gas-Insulated Substations.
IEEE C37.122-1 (2013) Guide for Gas Insulated Substations Rated Above 52 kV.
Gas Insulated Substations Book Edited by Hermann Koch.
https://www.omicronenergy.com
High-voltage Tests and Measurements during the Life Cycle of GIS Article Authors: U.Schichler,E. Kynast
On site tests of GIS S.M. Neuhold FKH Fachkommission für Hochspannungsfragen Zürich, Schweiz.